Catalytic nickel plating apparatus



H. R. NAcK cATALYTIc NICKEL PLATING APPARATUS Original Filed Dec. 9, 1952 MII United States Patent O CATALYTIC NICKEL PLATIN G APPARATUS rman R. Nac Troy Ohio assignor to The Common- Hewealth Enginegring ompany of Ohio, Dayton, Ohio,

a corporation of Ohio Application April 14, 195s, serial No. 504,811

s claims. (cl. 11s-4s) This invention relates to the deposition of metals from the gaseous statea More particularly the invention relates to the deposition of nickel from nickel carbonyls by thermal decomposition.

The deposition of nickel coatings on metals, such as iron and steels, has previously been practiced with varying degrees of success. Adhesion of the coating to the base metal, always a serious problem, has been achieved in a suitable manner for some applications. Eorts in the field have been directed to improving this adhesion in order that a product having a coating firmly bound to the base metal may be attained. These researches have considered the effects of various carrier gases for the carbonyls, the influences of flow rates, temperature, plating pressure, impurities, inter-gaseous decomposition, and so forth. The problem of securing a plate having suitable adherence to a base for all conditions of use however has remained present.

It has now been discovered that the adherence of the plating of nickel deposited from nickel carbonyl onto a base metal, such as iron and hot or cold rolled steels, may be materially improved, to the extent that a long thin sheet of the base when coated with nickel may be doubled upon itself without causing a buckling or separation of the coating from the base in any degree. In other words the coating and base remain completely integral under severe mechanical stress.

It is a primary object of this invention to set forth novel apparatus for the coating of bases with nickel carbonyl.

It is a further object of this invention to describe a novel treatment of hydrogen gas to enhance the properties thereof for treatment of a base metal.

These and other allied objectives ofthe invention are attained, generally speaking, by utilizing a catalyzed hydrogen gas both as a cleansing medium and as a carrier gas for the nickel carbonyl in the plating process.

The hydrogen gas in accordance with the precepts of this invention is itself exposed to, that is, is passed over, what may be termed active nickel a process which in some not completely analyzed manner enhances the action of the hydrogen. Thus it has been discovered that if a base metal to be plated is heated to a temperature in excess of 500 F. and hydrogen which has passed over freshly deposited nickelis brought into contact with the base metal, the surface thus prepared is very receptive to the metal of the nickel carbonyl upon seubsequent plating.

The active" nickel has been referred to as freshly prcpared; it is only necessary that the active nickel be pure metal-that is-unoxidized. Generally speaking we have found that a nickel deposit which has been exposed to air over a weekend and consequently oxidized is ineffective to condition the hydrogen gas for the attainment of the objectives of this invention.

It is to be noted however that nickel metal which is unoxidized may be utilized repeatedly in the production of plated objects without apparent loss of eliiciency. Thus, for example, a gas plating chamber may be fitted with a hollow steel cylinder coated on the interior with deposited nickel which has not been exposed to the atmosphere and the nickel contents of this tube will serve indefinitely to catalyze the action of the hydrogen gas passing therethrough.

The method of securing the nickel deposit is not critical but deposition from the gaseous -state is considered advantageous and as will hereinafter be described the nickel will be continually rejuvenated by the practice of the noted processes.

In the process of invention then the surface rendered receptive, by the exposure of the heated base metal to the atmosphere comprising the hydrogen passed over the active nickel, is, to effect metallic deposition thereon, exposed while heated to the action of hydrogen borne vapors of nickel carbonyl. This gaseous mixture is likewise passed over active nickel, that is, is exposed to the active nickel before or during the actual plating process.

./n important feature of the present invention is that the object to be plated need not be raised to unduly high temperatures to eect either the cleaning or the plating operation; thus with gun barrels it is generally desirable when plating the interior that the barrel itself be maintained at 750 F. or less. With the present invention the hydrogen gas passed over the active nickel may suitably and preferably be heated to much higher temperatures as l200 F. to 1500 F., and then brought in contact with the surface to be plated to eliect cleaning of the same; the body of the barrel may be at a much lesser ternperature, that is 500 F. and the slowly owing stream of hot hydrogen will not affect the body detrimentally. The resultant eiect however is the attainment of a surface eminently suitable for the receipt of the nickel coat.

The deposited nickel adheres tenaciously to the base metal and the thickness of the coat within normal limits has little or no effect upon the adhesion; this has been illustrated by preparing a thin coated sheet of hot rolled steel in accordance with the precepts of the invention and subjecting the sheet to severe bending sufficient to rupture the metal of the sheet-there was no apparent separation of the nickel from the base metal even at the rupture and the nickel could not be worked loose by prying at the same at the point of the rupture. Many processes for nickel deposition have been devised and investigated but no coating prepared by other methods has withstood this rigorous test; in fact, no other gas plating method has provided a bond which is at all analogous so far as is known.

With regard to the process of invention generally the usual precautions must be observed to obtain the improved adherent coat. Thus the object to be plated should be cleaned as thoroughly as possible prior to introduction to the plating chamber to remove surface oxides and other contaminants. Standard methods may be employed for this purpose and they include electroetching chemical processes, abrasion or a combination of these.

The nature of the metal to be plated determines to some extent the most satisfactory preliminary lcleaning method.` It has been found, for example, that hot rolled steel may be suitably prepared either by treatment with acid followed by an absolute alcohol wash or this chemical treatment may if desired be combined with an abrasion process. For cold rolled steel however the abrasion process is apparently necessary as this material does not respond quite as well when only the chemical treatment is employed. Thus while not critical the abrasion process possesses more advantages with some metals.

The preliminarily cleaned metal is then placed in a plating chamber and the same is exhausted to very low pressures. Where alcohol or equivalent material has been employed in the cleaning this is exhausted under vacuum. The exhaustion of the chamber and the removal of all occluded gas from the object is assisted by heating during evacuationthe heat being preferably applied though not necessarily by induction means.

The hydrogen gas is then bled slowly over the active nickel and to the object to be plated. The temperature of the object or base metal should be relatively highabove thenormal plating range for nickel carbonyl.

The exact nature of the mechanism between the nickel and the hydrogen and the influence of the so-treated gas upon the base metal is not known. The hydrogen, if untreated,'would as is known tend to clean the metal surface by a reduction process. However the degree of adhesion attained by this latter known method is not at all comparable, all other conditions being the same, to the effect of the treated hydrogen, and this has been established by repeated testing of both methods under varying conditions.

It has been theorized that the nickel provides active atomic hydrogen to some extent which then affects the base metal surface favorably. This is supported in some degree by the fact that as the temperature of the nickel to which the hydrogen is exposed is increased results appear to be more favorable. However even at the low temperature of 850 F. for the nickel improved results have been noted and for the present the explanation of the mechanism is in doubt.

'Ihe hydrogen is bled from a standard cylinder, treated and passed over the sample slowly-a rate of about M liter per minute measured at about 70 F. being satisfactory. The quantity and time vary somewhat with the size of the object but for a thin sheet 2" x 6" a time of about l0 minutes is thoroughly effective. Vacuum pumps are applied during all of this time and consequently the chamber pressure is maintained low assuring of rapid evacuation of all gases, that is, the hydrogen plus any impurities present. The application of vacuum is not however essential and the pressure in the chamber may be substantially or slightly greater than atmos-4 pherie-that is just suicient to insure of a hydrogen flow therethrough.

Thereafter nickel carbonyl in small quantity and the hydrogen, preferably but not necessarily mixed together, are passed over active nickel to the object. The temperature of the latter at .this stage should be relatively high, that is, above 500 F., and the temperature may be permitted to drop into the nickel carbonyl plating range of 250 F.450 F. during the in-ow of the gases. Care must be exercised however to avoid excessive decomposition of the carbonyl and it has been found that such does not occur when the gases are owed slowly, that is about -20 cc. per minute, and in small volume initially. Apparently the hydrogen inhibits premature carbonyl decomposition. As a result of this slow gas ow, a thin lm deposits on the activated metal surface, possibly resulting in diiusion of the nickel into the base metal as is indicated by the high degree of adherence attained.

It is to be noted that all ow rates unless otherwise specified are measured at room temperature conditions- 76 F. and atmospheric pressures.

As noted during the slow How of hydrogen and nickel carbonyl the temperature of the object is allowed to fall into the normal plating range of the carbonyl; the ow rate is then increased to about 1 liter per minute at a suitable carbonyl concentration and plating proceeds in normal manner, the entering gases however still preferably being passed through the active nickel, and where the active nickel is supported at a point remote from the workpiece the temperature of the nickel should be 100 F. or lessthat is below the plating range'.

The invention will be more fully understood by reference to the following detailed description and accompanying drawings wherein:

Figure 1 is a schematic view illustrating a complete apparatus useful in the preferred embodiment of the invention;

Figure 2 illustrates a modification of the invention;

Figure 3 illustrates a structural arrangement useful in one modification of the invention;

Figure 4 illustrates yet another structure useful in a further modification of the invention; and

Figure 5 illustrates a rigid qualitative test for adherence of the coat to the base metal.

Referring to the drawings and particularly Figure 1 there is shown at 1 a glass vessel having a removable stopper 3, an inlet 5 and an outlet 6. A water jacket 7 having an inlet 9 and outlet '11 substantially surrounds vessel 1. Positioned at the right hand end of the vessel is a small platform 13 on which may be mounted the base metal or hot rolled steel object 15 to be plated. Positioned at the left hand end of the vessel is a tubular member 17 coated internally with active nickel 19, the tube being supported in the vessel in any suitable manner as by member 21. Suitable induction heating coils 22, 24 surround the tube at the area of the support 13 and the support 21, respectively.

A conduit 23 for the passage of hydrogen and a conduit 25 for the passage of nickel carbonyl are illustrated at the far left of the figure and it is clear that gases passing through these conduits will contact the nickel 19 in the passage of the gases to the hot rolled steel object 15. The outlet conduit 6 terminates in a U-shaped portion 27 surrounded by Dry Ice or other cooling liquid 29 contained in a tank 31. The outlet of the portion 27 is connected to a vacuum pump to hasten the removal of gases from the vessel l.

In the operation of the apparatus indicated in Figure 1 with the vessel closed olf by valve 33 the vacuum pump is operated to completely remove gases from the vessel. During this period each of the coils 22, 24 may function to heat the interior components of the vessel to any suitable temperature to insure of the expulsion of all gases.

With valve 35 closed off valves 33 and 37 are opened to permit hydrogen to pass to the interior of the vessel 1. The temperature of the metal tube 17 and the nickel thereon is in excess of 850 F. and the upper limit is determined only by the temperature limits which the materials involved will stand. The temperature of the object 15 should also be in excess of 500 F. but may be considerably less than that of the cylinder 17. Specific data made under operating conditions are set out in the examples given hereinafter.

This arrangement of the apparatus offers the distinct advantage that in instances where the material 15 will not stand extremely high temperature, as in gun barrels, and where it is desirable to employ higher temperatures for cleaning, the hydrogen passing through the tube 17 may itself acquire a high temperature, thus increasing its activity to occasion a very beneficial effect on the object l5. It has been found that this arrangement is superior in such instances to that where the temperatures of the cylinder 17 and the workpiece l5 are equal.

The hydrogen gas activated by the nickel apparently completely frees the object 15 of all impurities and the vacuum pump is maintained in operation during all of this period in order that impurities developed will be removed promptly.

It should be noted in connection with the hydrogen that the gas employed in the experiments described hereinafter is tank hydrogen containing not more than 0.15% by weight of water and not more than 0.15% by weight of oxygen. During the passage of the hydrogen in the course of the above described cleansing operation, there is no evidence whatsoever of any oxidation of the object 15 as long as the hydrogen flow is maintained relatively low, that is at about 0.1 liter per minute. Under some conditions of very high hydrogen ow rates, that is from 2 to 3 liters per minute, it has been found that a hot rolled steel piece may on occasion turn slightly blue indicating an oxidation effect and this is to be avoided.

Normally the ow of hydrogen may continue for about 10 minutes to secure the beneficial action but as higher temperatures are employed the action is faster and the time may be shortened accordingly. Upon completion of cleaning the heating of object 15 is discontinued until the temperature falls to between 250 F.450 F. and it is then maintained at this level until plating is complete. However valve 35 is cracked open and nickel carbonyl is owed into the hydrogen stream and the mixed stream of hydrogen and carbonyl pass over the nickel 18 as the temperature of the object starts to drop. Some deposition of the nickel of the carbonyl gas may occur in the tube 17 but this is avoided to a great extent by initially owing the gas very slowly, that is, at about 10-20 cc. per minute into the vessel 1. Concentration of the carbonyl is about 35 percent of the gaseous mixture and apparently the large hydrogen concentration inhibits nickel carbonyl decomposition to some extent since cloudiness characteristic of premature decomposition is at a minimum.

It is to be noted in this connection that any nickel deposited in the tube 17 at 19 tends to keep the nickel rejuvenated. However as a practical matter the deposition in this area is very small, if any, and the carbonyl together with the hydrogen passes onto thel hot rolled steel piece 15 and nickel is deposited thereon.

The pump may be operated at all times during this initial ow of hydrogen and nickel carbonyl and the pressure is preferably maintained very low.

After the initial deposition of nickel the temperature of the workpiece is in the normal plating range of nickel carbonyl and is maintained at this level. The temperature of the nickel however is permitted to fall to 100 F. or less prior to heavy carbonyl flow to avoid excessive deposition at 17. The quantity of flow of hydrogen and the carbonyl is then increased to about 1 liter per minute the concentration of carbonyl being about 35%. The vacuum pump continues to operate in order to maintain the pressure within the vessel 1 low and nickel deposition continues to take place on the hot rolled steel piece 15 but at a faster rate. Some deposition may occur, as noted hereinbefore, at 19 but as indicated this is not detrimental in any respect. Upon completion of the plating to the desired thickness the stopper 3 is removed and the plated workpiece then taken from the chamber.

With the above described process a deposit of 3 mils may be obtained in about 20 minutes and other thicknesses may be obtained by merely increasing the time of plating.

It should be noted that the nickel 19 on cylinder 17 should not be exposed to the air during substitution of specimens or objects any longer than is necessary. Preferably to maintain optimum activity vacuum is maintained on the equipment as much as is possible.

The apparatus of Figure l and the opera-tion above described is preferred because it permits of operation of the cylinder 17 at a materially different temperature than the object 15. However it is to be noted that as illustrated in Figure 2 there may be substituted for the cylinder 17 a platen 30 which supports a workpiece 15.

This platen, preferably or steel, may be of any suitable metal coated with raised ridges of nickel 39 in order that the gases passing to the workpiece will contact the large surface of the nickel substantially as hereinbefore described.

It is also to be noted in connection with Figure 2 that the apparatus may if desired be operated without cooling. In this instance however it is desirable to maintain the ow rates as low as is consistent with production purposes in order to avoid excessive premature decomposition of the carbonyl. Where such decomposition occurs it will result in an inferior coating as far as adhesion is concerned. While such an arrangement-that is, without a cooling chamberhas been operated successfully it rcquires more attention and is not recommended in production operations.

The apparatus of Figure 2 illustrates that it is not essential that the gas ow contact the active nickel at any particular point of the system the mere presence of the active nickel during the hydrogen llow being sullcient to produce an activated surface which is receptive to the initial tlow of hydrogen and nickel carbonyl.

Figure 3 illustrates a metal tube 43 packed withsteel wool 45 having thereon a deposit of nickel and this may be substituted for the cylinder 17 of Figure l.

Figure 4 illustrates partially in section a similar metal tube 46, ,preferably of steel which contains suitably packed small steel balls 44 coated with nickel 47.

Figure 5 shows the manner of testing for adhesion and as will be noted a metal bar 49 (hot rolled steel) having a nickel coating 51 is severely bent to the point of fracture at 53. However even at -the edge 55 of the break ther:l is no apparent separation of the coat from the base met The following examples illustrate the process of inventionV and it is to be understood that they are presented as illustrative only and not as limitative of the inventive concept.

Example I Utilizing the apparatus of Figure 1 the following conditions prevailed during the plating operation as sequentially indicated:

Workpiece (base metal) Hot rolled steel Strip. Preliminary cleaning--- Ablrlaslon plus acid and alco- Heat u p time 10 minutes. workpiece temperature attained 650: F.

Cylinder temperature attained- 835 F. Hydrogen ow 10 min. at liter per mln. Work ieee temperature (during 625 F.-670 F. (gauge over hy rogen ow) 3 i t l o n s on e Cylinder temperature (during p p c 835 F. (maximum).

hydrogen iiow Coo workpiece to temperature Less than F.

Maximum 100 F. 330 11i-350" F.

1 liter per min.

of Cool cylinder to temperature 0 Hydrogen and nickel carbonyl 35%) while cooling Work ieee temperature Cylln er temperature Cool cylinder to lower than plating tem erature Maintain wor piece at Hydrogen and nickel carbonyl (35 a) introduced the cylinder must be below the temperature ofplatinlg2 of nickel carbonyl and preferably is about 100 The above process permits the deposition of .010" in 1 hour and the deposit is highly adherent as it withstand: the test indicated in Figure 5.

Example II The arrangement of Figure 2 is utilized in connection with the following procedure:

Work iece base metal) Cold rolled steel strip.

Prelixglnary( cleaning Abraslon lus degreasing in hot tric loroethylene treatmen Heat up time 10 minutes.

Workplece temperature attained 850 F. maximum. Platen tem rature 800 F.900 F 10 mln. at liter pexl mln.

750 F.850 F. (range over 3 points on piece).

900 F. maximum.

10-15 cc. per min. for 10 min.

Maximum 375 F.

Maximum 400 F.

at 330 F.s75 r'. Hydrogen and nickel carbonyl (35%) 1 liter per min.

During the initial introduction of carbonyl and during the platen operation itself some deposition of nickel on the nickel of the platen takes place. While this amount may be lost to production it serves to keep the platen rejuvenated and is accordingly beneficial in this respect.

An adherent deposit of about 3 mils may thus be obtained in about 20 minutes.

Example III Hydrogen ow--- Work ece temperature (during hy rogen flow) Platen temperature (during hydrogen ow) Coo work lece and platen to tempera ure of Hydrogen and nickel carbonyl (35%) while cooling Workglece temperature after car onyl introduction Platen temperature after carbonyl introduction Maintain workpiece and platen workpiece (hase metal) Cold rolled steel strip.

Preliminary cleaning Abraslon glue degreasing in hot tric loroethylene treatment.

Heat up time 12 minutes.

Workplece temperature attained 1000" F. maximum. Platen tem rature 1100 F 10 min. at fu liter per min.`

950 F.1050 F. (range over 3 points on piece).

hesion includes the contact of the activated metal base surface with the initial carbonyl gas flow while the base Hydrogen ow Work ece temperature (during hy rogen ow) Platen temperature (during hydrogen now) Coo workpiece and platen to temperature of Hydrogen and' nickel carbonyl (35%) while cooling Workglece temperature after car onyl introduction Platen temperature after carbonyl introduction Mailtaln workpiece and platen is above the normal plating range of 250 F.-450 F. for

the nickel carbonyl. Apparently such contact insures that completely repetitive results will always be attained as far as adhesion is concerned. n the other hand in one instance where the carbonyl was not passed to the workpiece until the same was at a temperature in the lower end of the plating range the coating was not up to the usual standard.

It is also to be noted with regard to the specitc data on platen and workpiece temperature that such measurements were made by thermocouples the leads of which pass through the chamber walls; the slight variations in maximum temperature between the workpiece and platen where the same are on contact are occasioned by the contour of the coil with respect to these elements. As readings were taken at 3 points on each of the surfaces the figures set out are considered to be completely representative of actual conditions.

This application is related to copending application of Herman R. Nack, et al., Serial No. 324,962, filed December 9, i952, now Patent No. 2,731,361, and assigned to the same assignee as the present invention and wherein there is described a process for the utilization of carbon monoxide in conjunction with active nickel in the gas plating process.

It will be understood that this invention is susceptible to modiiication in order to adopt it to different usages and conditions and accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

I claim:

l. Apparatus for gas plating comprising a chamber having an inlet and an outlet, means for passing a' gas through the chamber from the inlet to the outlet, support means within said chamber to position a workpiece therein, and a body of active nickel supported within said chamber between said support means and said inlet to contact a gas iiowing from said inlet to a workpiece on said support means. n

2. In combination, in gas plating apparatus, a vessel having an inlet and an outlet, support means within the vessel for a workpiece to be plated, means for connecting said inlet to a source of a gas to be heated, a body of active nickel in the vessel arranged to be contacted by a gas owing into said vessel through said inlet, means to heat said body of active nickel to thereby heat a gas flowing over said nickel, the support means being arranged between the inlet and outlet of the vessel and in the path of a gas heated by said nickel.

3. In gas plating apparatus, the combination of a vessel having an inlet and an outlet, support means within said vessel to position a workpiece within the vessel, a body of active nickel supported within said vessel between said support means and said inlet to contact the gas owing from said inlet to a workpiece on said support means, heating means surrounding said support means, and heating means surrounding said body of nickel.

4. In gas plating apparatus, in combination, a longitudinally extending vessel having an inlet at one end thereof and an outlet adjacent the other end thereof, support means within said vessel to position a workpiece between the inlet and outlet of said vessel, heating means surrounding said support means, a body of active nickel positioned between the support means and the inlet of the vessel, heating means surrounding the body of active nickel, means for connecting said 'inlet to a source of hydrogen gas, and means for passing said hydrogen gas through said vessel.

5. In gas plating apparatus, in combination, a vessel having an inlet and an outlet for the passage through said vessel of a gas, support means within said vessel to position a workpiece therein, said support means being between said inlet and said outlet and arranged to be in the path of a gas flowing from said inlet to said outlet, a body of active nickel between the inlet and the support means, the body of active nickel being arranged to be contacted by a gas passing to said support means, means to connect said inlet to a source of hydrogen gas, and means to connect said inlet to a source of nickel carbonyl, the body of active nickel and the support means each having heating means surrounding the same.

6. In apparatus for gas plating, the combination of a vessel having an inlet and an outlet, means for passing a gas through the vessel from the inlet to the outlet, support means within said vessel between said inlet and outlet for positioning a workpiece in the vessel, a body of active nickel supported within said vessel between said inlet and said outlet, a water jacket surrounding said vessel, heating means around said jacket at said support means, heating means around said jacket at said body of active nickel, means for connecting said inlet to a source of hydrogen gas, the means for passing the gas through thelvessel including a vacuum pump connected to the out et.

References Cited in the tile of this patent UNITED STATES PATENTS 1,113,151 Chisholm Oct. 6, 1914 2,293,946 Payne Aug. 25, i942 2,408,164 Foster Sept. 24, 1946 2,526,657 Guyer Oct. 24, 1950 

3. IN GAS PLATING APPARATUS, THE COMBINATION OF A VESSEL HAVING AN INLET AND AN OUTLET, SUPPPORT MEANS WITHIN SAID VESSEL TO NPOSITION A WORKPEICE WITHIN THE VESSEL, A BODY OF ACTIVE NICKEL SUPPORTED WITHIN SAID VESSEL BETWEEN SAID SUPPORT MEANS AND SAID INLET TO CONTACT THE GAS FLOWING 